The invention relates generally to hook-lift hoists mounted on a wheeled chassis and, more specifically, to a hook-lift hoist that has a lifting capacity that is less than its dumping capacity.
Hook-lift hoists have been in common use, particularly in European countries, for a number of years. The hoist has a pivotable L-shaped arm with a hook on its distal end portion that is used to engage a detachable truck box. The arm is pivoted to lift the box onto the chassis for transport of the box and its contents to any location.
It has become known also to provide the truck chassis with a lift mechanism for tilting of the box atop the chassis to dump the contents of the box rearwardly of the truck. Hook-lift hoists allow for a single truck chassis to be used with a wide variety of truck boxes, each of which has a distinct and advantageous use. A single truck chassis with a hook-lift hoist can be used, for example, to load, transport and dump open-topped waste receptacles to a disposal site; to load, transport, and unload shipping containers; to mount, use, and dismount road maintenance equipment, such as a salt spreader; to load, transport, and unload wheeled equipment; and so on. This functional versatility makes hook-lift hoists an economical vehicle for transport industries, particularly the street and highway maintenance departments of municipalities, states, and other governmental entities where budgetary constraints and the variety of tasks that must be performed make these multi-purpose vehicles an attractive choice.
Known hook-lift hoists have the limitation that the lifting capacity is the same as the carrying and dumping capacity of the vehicle. The lifting capacity, or loading capacity, of a hook-life hoist is the weight of the heaviest object the hoist can move from a detached ground-supported position to a loaded position on the truck chassis. The lifting or loading capacity of a chassis is the heaviest object the chassis can load without the front wheels of the chassis becoming unloaded. The carrying capacity of the vehicle is the maximum weight that can loaded on the vehicle and still have the vehicle remain safe to transport the loaded weight. The dumping capacity of the vehicle is the weight of the heaviest object which the hoist lift can tilt to an off-loading position. Because the maximum amount a truck can lift may be less than the maximum amount it can carry and dump, particularly for short wheelbase, maneuverable trucks, the capabilities and usefulness of these hook-lift hoists is diminished. For a given size, weight, and horsepower of truck, its carrying and dumping capacities are not fully utilized. This excess capacity reduces the economy of these single capacity hook-lift hoists.